This project has as its objectives the determination of the extent to which the chemical energetics and mechanical behavior of muscle conform to the expectations based on the biochemical properties of the contractile proteins and relaxing factor system, the structural features as embodied in the sliding filament hypothesis and physiological characteristics of the excitation-contraction coupling system. Energy fluxes are determined by following the rates of heat production, structural and physiological characteristics are established by examining the dependence of the energy fluxes on physical, chemical, and mechanical parameters.